In the pickling of high-grade-steel hot-rolled strip (DE 195 05 324 C2), the high grade steel strip is passed through an annealing and pickling line. Prior to the pickling a descaling is effected which involves two processing segments: blasting and pickling. In the blasting, the strip surface is mechanically descaled in that particles impinge upon the strip surface which remove the scale because of their kinetic energy. It is known to include in some annealing and pickling lines an additional stretch leveller so as to improve strip quality with respect to the planarity of the strip on the one hand and on the other hand to produce cracks in the scaling layer which facilitates the later chemical pickling process. Following the mechanical preliminary descaling steps, a wet chemical pickling is carried out. This pickling process can, depending upon the apparatus configuration, comprise a plurality of steps. For purely hot-rolled strip as a rule the pickling involves a sulfuric acid prepickling with residual descaling being effected in an acid mixture of nitric acid and hydrofluoric acid.
This known process is disadvantageous because of the use of the blast method which increases the roughness of the strip surface and thus reduces strip quality. In addition, the operating cost because of the use of the acid mixture and especially the hydrofluoric acid is very high.
The method described at the outset is known (EP 0 706 840 A2) for the production of high-quality cold-rolled steel strip carried out inline with the working steps directly following one another of descaling the roughed out strip, reducing the roughed out strip to final thickness, annealing and pickling.